The present invention relates to polybenzimidazole resins useful as the stationary phase in chromatographic processes such as ion-exchange, purifications, separations, etc., and as polymeric catalysts and chemical reagents useful in polymer supported chemical reactions. It particularly relates to polybenzimidazole resins in microporous particulate form which possess improved performance characteristics in processes of the above types as compared with previously known forms of polybenzimidazole.
As used herein, the term "chromatographic processes" is used in a generic sense referring to processes of the type wherein a mobile phase (gas or liquid) is contacted with a stationary phase, comprising the novel microporous polybenzimidazole particulates of this invention. Accordingly, while as will be described more fully hereinafter the instant polybenzimidazole particulates possess ion-exchange characteristics, the scope of the present invention is not limited to processes which rely on an ion-exchange mechanism, but includes within its scope other processes, well known to those skilled in the art such as separations, purifications, etc., which rely on the polarity, adsorptivity and/or acid/base characteristics of the invention polybenzimidazole particulates.
Polybenzimidazoles (hereinafter referred to as PBI) are a well known class of polymers characterized by a high degree of thermal stability, chemical resistance and toughness. As a result of these properties, PBI has found application in a wide variety of uses, such as replacements for asbestos in high temperature applications such as gloves, conveyor belts and plastic composites. In addition, a sulfonated, textile grade, PBI fiber has been developed by the assignee of the subject application for use, inter alia, in high performance fabrics. See Textile Research Journal, Vol. 52, No. 7, pages 466-472 (July 1982).
Due to its excellent thermal and chemical resistance properties, PBI has also been suggested for use in semi-permeable membranes (see U.S. Pat. Nos. 3,699,038; 3,720,607; 3,851,025; and 4,020,142), as well as in substrates for chromatographic processes (see U.S. Pat. Nos. 3,560,158 and 3,408,336). The possibility of developing a PBI substrate useful in chromatographic processes has been particularly attractive to the art since the resins commonly used for this purpose, such as the crosslinked styrene copolymers possess less than satisfactory chemical and thermal stability. Prior art attempts to develop such PBI substrates have been largely unsuccessful, however.
While as can be seen from U.S. Pat. Nos. 3,408,336; 3,560,158; and 4,394,500, particulate forms of PBI having a shape useful for chromatography applications have heretofore been prepared by those skilled in the art, the particulates described in those patents are not disclosed as having a microporous structure. As is well known to those skilled in the art, resins useful in chromatographic procedures such as ion-exchange should desirably possess a high porosity and preferably have a macroreticular or other highly porous structure. Resins which do not possess such porosity do not possess sufficient surface area to provide chromatographic capacities competitive with the conventional resins employed in chromatography such as the crosslinked styrene copolymers marketed by, e.g., Rohm & Haas Company under the tradename Amberlyst..RTM.
In addition, the practical utility of the PBI substrates heretofore known in the art in chromatographic processes such as ion-exchange has been further limited by the fact that PBI possesses only weakly basic anion exchange characteristics. In contrast, the conventional resins used in chromatographic procedures such as the cross-linked styrene copolymers are available in both anion and cation exchange forms having a wide range of acidities/basicities.
In addition to PBI and the Amberlyst.RTM. type resins, other resins have also been suggested by the prior art for use in chromatography applications. Anion exchange resins of the weakly basic type containing nitrogen heterocyclic rings, for example, have been described in U.S. Pat. No. 3,311,572. Such resins comprise crosslinked copolymers formed by copolymerizing using emulsion techniques, a nitrile-containing vinyl monomer, a polyvinyl monomer and a nitrogen-containing diamine heterocycle compound such as imidazoline or tetrahydropyrimidine. It is disclosed that polymer beads having a porous macroreticular structure may be obtained by including a diluent in the polymerization recipe which acts as a precipitant for the resulting copolymer. Such anion exchange resins do not possess PBI's excellent thermal stability, however, and thus are not desirable for use in high temperature applications.
Crosslinked bead copolymers prepared by pearl copolymerization of 4-vinylpyridine, styrene and divinylbenzene, functionalized by reaction with various acids have also been suggested for use as reagents in polymer supported chemical reactions (See, Journal of Macromolecular Science-Chemistry, A 11 (3), pages 515-534 (1977); and Journal of Organic Chemistry, Vol. 43, No. 13, pages 2618-2621 (1978)), as well as acid scavengers in non-aqueous systems.
In addition, the prior art has suggested that fibers prepared of benzimidazole-terephthalic acid copolymer, complexed with metal ions, may be used as ion-exchangers. While useful for some purposes, fibers are not desirable for use in chromatography due to the generation of higher back pressures than those encountered with polymers in bead form. In addition, as noted above, useful polymeric supports desirably possess a high porosity.
As can be seen from the foregoing discussion, the prior art has yet to develop a PBI material which combines the attractive chemical and physical properties of PBI resins with a form which is useful in chromatographic processes or supported chemical reactions or syntheses.